[The chicken beta-globin genes: a model system for studying transcription regulation at the level of genomic domains]

In the last quarter of the XX century, as a result of studies performed on a number of model systems, a hypothesis was formulated according to which the genome of higher eukaryotes consists of functionally isolated areas named genomic domains. Each domain includes one or more genes and a regulatory system that is normally active only in respect of this domain and allows it to achieve the regulatory autonomy of the neighboring chromosome regions. A genomic domain is characterized by the spectra of covalent histone modifications which define the boundaries of the domain and the degree of chromatin condensation within it, and so, the probability of transcription activation of genes within the domain. Development of the domain hypothesis of genome organization became possible to a large extent through the study of mechanisms of transcriptional regulation of the globin genes in vertebrates. One of the most popular models in this field of molecular biology is the chicken beta-globin gene domain. Based on this model system, the fundamental principles of complex enhancer action in higher eukaryotes have been described, the properties of insulators and functional units of enhancers and promoters have been studied, the influence of covalent histone modifications on the level of chromatin condensation and their role in the regulation of transcription within the domain have been investigated. In this review we summarize the data on the study of the chicken beta-globin gene domain, as well as consider the domain hypothesis of eukaryotic genome organization.